This invention relates to an expandable piston motor utilizing rotary valves.
Expandable piston motors, also referred to as variable compression ratio (VCR) motors, are disclosed in such earlier U.S. Pat. Nos. as 2,910,826 and 3,200,798 to Mansfield, 3,161,112 to Wallace, 3,185,137 to Dreyer, 3,185,138 to Druzynski and 3,303,831 to Sherman. These patents disclose pistons which include an outer portion with an inner portion slidably received therein. The connecting rod is connected to the inner portion and there is a chamber between the inner and outer portions adjacent the crown of the piston. A passage in the connecting rod supplies oil from the lubrication system to the chamber. These motors usually rely upon the inertial tendency of the outer portion of the piston to move upwardly relative to the inner portion at the end of the exhaust stroke in order to move the lubricating oil into the chamber. U.S. Pat. No. 3,200,798 employs a pump mechanism for this purpose. To prevent a reverse flow of lubricant, nonreturn valves are usually fitted. In order to discharge oil from the chamber, a discharge valve is activated at a predetermined pressure in most such engines.
The lubricating oil filling the chamber raises the outer portion of the piston relative to the inner portion to increase the compression ratio and thereby improve the efficiency of the engine. This would occur if the engine is operating at part throttle when the pressure in the combustion chamber would normally be less than optimum. When the pressure is increased to the optimum amount, or the design limits of the engine, the oil is released from the chamber through the discharge valve.
The engines disclosed in the previous patents listed above do not provide any mechanism for precisely timing the intake and discharge of lubricating oil to and from the chamber. Moreover, they rely upon a plurality of valves in each piston to regulate the flow of oil.